1. Technical Field
The present invention relates to nitride semiconductor light-emitting devices.
2. Description of the Related Art
Japanese Unexamined Pat. App. Pub. No. H10-22525 describes nitride light-emitting devices that emit light of any chromaticity (color saturation, color phase) per unit pixel, and particularly that emit pure white light. One example of a nitride light-emitting device in Japanese Unexamined Patent App. Pub. No. H10-22525 is furnished with a first multiple quantum well composed of a (trilaminar) 5-nm thick In0.68Ga0.32N well layer, and a (quadrilaminar) 5-nm thick In0.1Ga0.9N barrier layer, and with a second multiple quantum well composed of a (trilaminar) 5-nm thick In0.3Ga0.7N well layer, and of 5-nm thick In0.05Ga0.95N barrier layers. The first multiple quantum well emits yellow-green light with a peak wavelength of 570 nm, and the second multiple quantum well emits blue light with a peak wavelength of 450 nm. The second multiple quantum well lies between the first multiple quantum well and a transparent electrode. The wavelength components of light from the first multiple quantum well are complementary colors for the wavelength components of light from the second multiple quantum well.
A different example of a nitride light-emitting device in Japanese Unexamined Pat. App. Pub. No. H10-22525 has a first multiple quantum well that comprises In0.5Ga0.5N well layers and exhibits a peak wavelength of 510 nm, a second multiple quantum well that comprises In0.46Ga0.54N well layers and exhibits a peak wavelength of 500 nm, and a third multiple quantum well that comprises In0.43Ga0.57N well layers and exhibits a peak wavelength of 490 nm. With this nitride light-emitting device, nearly pure white light can be obtained.
In Japanese Journal of Applied Physics, Vol. 41, 2002, pp. L1431-L1433, InGaN light-emitting diodes are described. Referring to FIG. 5 of the publication, the quantum efficiency of InGaN light-emitting diodes varies depending on the injected current density, and in particular, the quantum efficiency of blue-light emitting diodes varies greatly in accordance with the injected current density.
In each of the nitride light-emitting devices in Pat. App. Pub. No. H10-22525 the wavelength of light from one of the multiple quantum wells differs from that of light from the others, meaning that in none of the nitride light-emitting devices does the progression of the spectral-component magnitudes change independently of the density of the current injected into the devices.
As set forth in Japanese Journal of Applied Physics, ibid., the quantum efficiency of InGaN light-emitting devices varies in accordance with the injected current density, and in particular, the quantum efficiency of blue-light emitting diodes varies significantly depending on the injected current density.